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48

Water is essential not only to survival but is also equally or even

more important than nutrients in food production. Agriculture ac-

counts for nearly 70% of the water consumption, with some es-

timates as high as 85% (Hanasaki

et al

., 2008a,b). Water scarcity

will affect over 1.8 billion people by 2025 (WHO, 2007). This could

have major impacts on health, particularly in rural areas, and thus

also major impacts on farmer productivity. Although of great sig-

nificance, such indirect effects are not considered here. Current

projections suggest that water demand is likely to double by 2050

(Figure 20). Estimates project water withdrawals to increase by 22–

32% by 2025 (De Fraiture

et al

., 2003) and nearly double by 2050,

for all SRES scenarios (Shen

et al

., 2008). For poor countries with

rapid population growth and depletion of groundwater, water-defi-

cit induced food insecurity is a growing problem (Rosegrant and

Cai, 2002; Yang

et al

., 2003). One major factor beyond agricultural,

industrial and urban consumption of water is the destruction of

watersheds and natural water towers, such as forests in watersheds

and wetlands, which also serve as flood buffers (UNEP, 2005).

IMPACTS OF WATER SCARCITY ON YIELD

Studies of 128major river basins and drainage regions show

that approximately 20 to 50% of the mean annual river flow

in different basins needs to be allocated to freshwater-de-

pendent ecosystems in order to maintain them in good eco-

logical condition. In large parts of Asia and North Africa

and some parts of Australia, North America and Europe,

current total direct water withdrawals (primarily for irriga-

tion) already tap into the estimated environmental water re-

quirements (Smakhtin

et al

., 2004). The global consump-

tion of both “blue’’ water (withdrawn for irrigation from

rivers, lakes and aquifers) and “green’’ water (precipitation)

by rainfed and irrigated agriculture and other terrestrial

ecosystems is steadily rising (Rost

et al

., 2008).

Water is probably one of the most limiting factors in increas-

ing food production. Yields on irrigated croplands are, on

average, 2–3 times higher than those on rainfed lands. Ir-

rigated land currently produces 40% of the world’s food on

17% of its land (FAO, 1999), most of it downstream and de-

pendent upon glacial and snowmelt from the Hindu Kush

Himalayas. It is evident that in regions where snow and

glacial mass are the primary sources of water for irrigation,

such as in Central Asia, parts of the Himalayas Hindu Kush,

China, India, Pakistan and parts of the Andes, melting will

eventually lead to dramatic declines in the water available for

irrigation, and hence, food production (Figure 21).

The melting glaciers will impact certain countries more than

others, and also substantially impact hydropower production.

The Indus River and its tributaries, for example, in addition

to providing nearly 60% of the water utilized for irrigation,

also provide 45% of the electrical energy in Pakistan.

Of great importance, therefore, is the effect of climate change

on the extent of snow and glacial mass (UNEP, 2007) and

on the subsequent supply of water for irrigation. Climate

change could seriously endanger the current food produc-

tion potential, such as in the Greater Himalayas Hindu Kush

region and in Central Asia (Figure 21). Currently, nearly 35%

of the crop production in Afghanistan, Bangladesh, Bhutan,

China, India, Myanmar, Nepal and Pakistan is based on ir-

rigation, sustaining over 2.5 billion people. Here, water de-

mand is projected to increase by at least 70–90% by 2050.

Increase, over 2002

water requirements,

needed to meet the

2015 hunger target

Increases, over

2002 water

requirements,

needed to eradicate

poverty by 2030 and

2050 respectively

2 000

0

4 000

6 000

8 000

1960

1970

1980

1990

2002

2015

2030

2050

Water requirements

for food production

(km

3

/year)

Figure 20: Historic and projected changes in water consumption for

food production, 1960-2050.

(Source: ).